Acoustic diaphragm



April 21, 1936. N. E. WUNDERLICH ACOUSTIC DIAPHRAGM Original Filed May16, 1930 Patented Apia 21,1936 I PATENT OFFICE ACOUSTIC DIAPHRAGM NormanE. Wunderlich, West Collingswood, N. 8.,

- assignor, by mesne assignments, to Radio Corporation of America, NewYork, N. Y., a corporation of Delaware Application May 16, 1930, SerialNo. 452,856 In Great Britain June 20, 1929 9 Claims. (Cl. 179-1155) Thisinvention relates to diaphragms for acoustic instruments andparticularly to a coil mounting and centering means for conicaldiaphragms as found in reproducers of the type known in the art aselectrodynamic speakers.

The primary object of the invention is to provide an acousticdiaphragmof the character described, which lends itself readily togreater mass production in manufacture, thru the elimination of aplurality of part assembly steps, thereby proportionately reducing thecost of manufacture. The accuracy of the finished product is increasedby the further elimination ofvpossible error in positioning and joininga plurality of parts with respect to each other so as to have a commoncenter.

Further in accordance with the invention it is an object to simplify thegeneral practice heretofore in the art, of separately attaching adiaphragm mounting and centering disc or spider and a cylindricaldriving coil mounting, to a conical element comprising an acousticdiaphragm, or alternatively, attaching an assembled or integral unitcomprising a centering disc and a cylindrical driving coil mounting, toa conical diaphragm as aforesaid.

Further in accordance with the invention, a conical acoustic diaphragmis provided with a cylindrical extension or flange for concentricallylocating and supporting a diaphragm driving coil structure and a flatflexible disc is provided for supporting and centering the actuated ordriven end of said diaphragm, includingthe centering of said coil, withrespect to and in co-operative relation with an electro-magnetic fieldelement, said extension and disc forming an integral part of the conicalportion comprising the acoustic diaphragm.

Accordingly, the invention resides in the novel formation of an acousticdiaphragm so as to include a driving coil supporting means and a flatflexible centering means as an integral part of the diaphragm after theformation thereof from a flat sheet of material. 4

While one practical embodiment of the invention has been illustrated anddescribed, it is to be expressly understoodhowever, that the annexeddrawing forming a part of this specification, is intended for purposesof illustration only, and-is not to be construed as a definition of thelimits of the invention, reference being had to the appended claims forthat purpose.

Referring in detail to the annexed drawing wherein like referencecharacters areemployed to designate corresponding parts,

Fig. 1 is a sectional view of a frusto-conical diaphragm formed inaccordance with the preferred form of the invention and assembled inco-operative relation with a fragmentary portion of a field magnetelement therefor.

Fig. 2 is a fragmentary sectional plan view of a modified form of thediaphragm centering surface shown in Fig. 1, looking in the direction ofthe closed end portion of. the conical diaphragm.

Fig. 3 is a view similar to Fig. 2, illustrating a further modification.

Fig. 4 is a fragmentary sectional view similar in part to Fig. 1,illustrating a further modification wherein the driving coil is wounddirectly on an integral part of the frusto-conical diaphragm.

Referring to the drawing, an electro-dynamic reproducer or loud speakerof the conventional inner core and outer annular ring magnet type,sufliciently complete for the purpose of this invention, is illustratedin Fig. 1, wherein inner and outer pole pieces ill and l I designate thecore and ring pole piece of the field magnet respectively, and whichtogether form an annular magnetic field or air gap as indicated at l2.

As usual in-structures of this character, the core I0 is tap screwthreaded at the center of its free end for the reception of a suitablescrew or the like l3, whereby, in conjunction with suitable washers N,forms a stationary support for the driven end of the conical diaphragml5, and an actuating coil structure including a mounting or form IS. Thecoil structure is centralized on the core II), with respect to and invco-operative relation with the annular air'gap I2.

The opposite or base end of the conical diaphragm I5 is, as usual,mounted over an aperture I! in a baflie plate l8, or on the inner sideof the front panel of a cabinet (not shown) by means of a number ofarcuate sections 19, for example three, of leather, fabric or the like,having a total 4 length greater than the periphery of the base of thecone. These strips are suitably secured on the one hand to the baiiieplate l8 by means of, a'suitable annulus 20, and on the other, to thebase edge of the conical diaphragm in a manner well known to thoseskilled in the art.

Theadiacent free ends of the arcuate flexible strips or sections l9. arepermitted to overlap loosely as indicated at 2|, for example, andthere-' fore arenot cemented together. This has been found to be asatisfactory and economical method of securing the base edge of theconical diaphragm.

-More particularly in accordance with the invention, a diaphragm for areproducer structure 5 the passage therethru I plated.

mation by moulding or pressing a flat sheet of I material preferablybuckram, cheesecloth or other suitable fabric, which has been damped j.with any well known sizing material, by means of heated dyes, to deformthe flat sheet, of material into conical form.

In this pressing operation, however, the diaphragm is given twoadditional formations other than conicaL- One of these additionalformations consists of a cylindrical coil structure locating andsupporting cylindrical flange 22 which is formed during the singlepressing operation as an integral part of the conical portion comprisingthe diaphragm l5, and particularly adapted in this the preferred form,for the attachment thereto of the actuating coil mounting l6 by means ofa suit-- able adhesive.

The other one of said additional formations consists of a small areacentrally of the diaphragm which remains flat in the said pressingoperation and forms a coil centering flexible disc like element 23disposed in a plane normal to the axis of the conical diaphragm l5, andwithin the aforesaid supporting flange 22.

In order that the driven end of the conical diaphragm l5 may be attachedto the free end of the core ill by means of the screw I 3, it isdesirable to form an aperture 24 centrally of the disc like surface 23of suflicient size to permit of the threaded portion of the screw i3.Accordingly, the said aperture 24 may be blanked out simultaneously withthe formation of the conical diaphragm IE, or, it may be formed as asecondary operation after the pressing of the conical diaphragm has beencom- Referring particularly to Fig. 2, the flat flexible and imperforatecentering surface 23a is modified by providing a plurality of annularcorrugations 25 in the said centering surface, or alternatively as shownin Fig. -3, the surface is perforated by means of a'plurality ofopenings or holes 26 circumferentially disposed radially of the aperture24 in the centering surface 23b, whereby a greater degree of flexibilityis imparted to the said cen- 1 tering surface between its center pointof attachment and the periphery thereof. These modified forms impart agreater freedom of longitudinal or axial movement to the diaphragmwithout unduly reducing the lateral stiffness of the disc, if this isfound necessary or desirable.

A further modification is illustrated in Fig. 4,

wherein it will be readly seen that the cylindrical portion 22 describedin connection with Fig. 1 is much more pronounced, that is to say, thecylindrical portion projects a greater distance beyond the smallerconical portion of the diaphragm i5 to provide an integral cylindricalmember 220 whereon the diaphragm actuating coil 2| may bedirectly wound.This may be accomplished by placing the entire cone i5 upon a suitablemandrel and forming the coil 21 on the freeend portion of thesaidcylindrical member. Accordingly, the usual attachment of a separatecylindrical coil carrying support to a conical diaphragm of thecharacter described is eliminated.

Further withrespect-to Fig. 4, it will also be observed that'theflexible centering surface 230 in this form is disposed withinthecylindrical coil support, since the cylindrical projecting member 220carrying the coil 21 extends inwardly beyond the free end of the inner.pole or core ID to which the centering surface is attached by means ofthe permit of free longitudinal washers u and I: so that the an :1

- will bedisposed within the air gap i2.

The flexible centering surface 230 is formed within the cylindrical coilsupport (see Fig. 4) by telescopically reversing the free end portion ofthe integral cylindrical extension 220 within itself in the moulding orpressing of the diaphragm ii. In telescopically reversing the free endportion of the integral cylindrical extension 220 part way withinitself, the wall of the said free end portion is doubled since thewallthickness thereof will then consist of .two thicknesses of the sheetmaterial used for moulding or pressing a conical diaphragm therefrom.This particular operation incidentally enhances the rigidity of the coilreceiving portion of the said free end portion for the coil formingoperation as aforesaid.

After the diaphragm moulding operation has been completed, the conicaldiaphragm is preferably subjected to a moisture proofing treatment suchas for example with an aluminum paint or the like, thereby rendering thediaphragm substantially non-hygroscopic.

What is claimed is:

1. A unitary sound reproducing diaphragm comprising a frusto-conicalsurface and a cylindrical surface, the smaller base of said conicalsurface merging into said cylindrical surface, said cylindrical surfacehaving a corrugated centering disc in a plane normal to the axis of saiddiaphragm.

2. As an article of manufacture, a frusto-conical diaphragm the apex ofwhich merges into a cylinder having a closedend, the closed end beingtelescopically reversed into the cylindrical portion to provide acentering disc.

3. The invention defined in claim 2 characterized in that a voice-coilis wound upon the outer surface of the cylinder.

. secured to the small base of said diaphragm,

a corrugated imperforate coil-centering diaphragm-supporting disc ofthin flexible material,

and a stationary support for a portion of said disc.

5. A sound-producing device comprising in combination, a frusto-conicaldiaphragm flexibly supported at its large base, an actuating coilsecured to the small base of said diaphragm, a cor-' rugatedcoil-centering diaphragm supporting disc of thin flexible material, andastationary support for a portion of said disc, the corrugated portionof said disc having suflicient radial length 'to movement thereofwithout unduly reducing -the lateral stiffness of the same.

6. A sound-producing device comprising in combination, a frusto-conicaldiaphragm flexibly supported at its base, an actuating coil secured tosaid diaphragm, a coil-centering diaphragm-supporting disc of thinflexible .material provided with concentric corrugations, and astationary support for a portion of said disc, the corrugated portion ofsaid disc having suflieient radial length to permit of free longitudinalmovement thereof without unduly reducing the lateral stiffness of thesame,

'7. In a sound-producing device having a diaphragm flexibly supported atits base and an actuating coil secured thereto, a coil-centeringdiaphragm-supporting discof thin flexible substantially non-hygroscopicmaterial provided with concentric corrugations, and a stationary supportfor a portion of said disc, the corrugated portion of said disc havingsufiicient' radial'length to permit of free longitudinal movementthereof without unduly reducing the lateral stiffness of the same.

8. A sound-producing device comprising in combination, a cone diaphragmflexibly supported at its base, a magnet having a core and a polepiece,a coil support, an actuating coil carried by said support, said coilbeing disposed in the air gap between said core and pole-piece and saidcoil-support being secured to said diaphragm, a thin disc for centeringsaid coil provided with concentric corrugations, said disc being ofthinflexible material and having a portion for receiving said coil support,and a stationary support for another portion of said disc, thecorrugated portion of said disc having sufficient radial length topermit of free longitudinal movement thereof without unduly reducing thelateral stiffness of the same. A

9. A sound-producing device comprising in I combination, a conediaphragm. flexibly supported disposed in the air-gap between said coreand pole-piece and the corrugated portion of said disc having suflicientradial length to permit of free longitudinal movement thereof withoutunduly reducing the lateral stiffness of the same. NORMAN E. WUNDERLICH.

